1. Field of the Invention
The present invention relates to an LC parallel resonator and a multilayer band pass filter including a plurality of the LC parallel resonators.
2. Description of the Related Art
Known examples of high-frequency band pass filters which are appropriate for reducing size and cost include a multilayer band pass filter. An example of a multilayer band pass filter is disclosed in the International Publication No. 2007/119356. In this multilayer band pass filter, a plurality of LC parallel resonators are provided within a multilayer body which includes a plurality of dielectric layers stacked on top of one another. In each of the LC parallel resonators, a loop inductor electrode, starting from a connection point connected to a capacitor electrode, includes line electrodes and inter layer connection conductors (via electrodes). In this multilayer band pass filter, areas (hereafter, also called loop surfaces) surrounded by a loop defined by the corresponding inductor electrode of the LC parallel resonators are superposed with one another. Thus, magnetic coupling between the inductor electrodes of neighboring LC parallel resonators can be enhanced such that a wider band is achieved.
In order to obtain desirable characteristics in a multilayer band pass filter including a plurality of LC parallel resonators, it is necessary to reduce the parasitic resistance of the inductor electrodes and reduce the insertion loss of the multilayer band pass filter.
Examples of methods of reducing magnetic coupling between neighboring LC parallel resonators include a method in which neighboring LC parallel resonators are displaced in the stacking direction of dielectric layers, so as to reduce overlapping between the loop surfaces, a method of inserting a dielectric layer (capacitance layer) which includes a capacitor electrode arranged so as to be superposed with a line electrode when viewed in the stacking direction, and others.
Even when magnetic coupling between LC parallel resonators is reduced, when the size in the stacking direction is increased, the length of a signal path is increased, such that the parasitic resistance of a via electrode is increased and the Q factor may be decreased. As a result, the insertion loss may be increased.